Formulating Biocontrol Agents for Saskatchewan Conditions



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Saskatchewan

Agriculture

and Food

Saskatchewan Agricultural Development Fund

ADF Project 9900053, Res 92BW

The Impact of Herbicide Mode of Action on Low-Drift Spray Effectiveness

Progress Report

February, 2002

Tom Wolf1, Rick Holm2, Ken Sapsford2, Linda Hall3, and Rene Van Acker4

1 Agriculture & Agri-Food Canada, Saskatoon

2 University of Saskatchewan, Saskatoon

3 Alberta Agriculture, Food and Rural Development, Edmonton

4 University of Manitoba, Winnipeg

Abstract

The second year of a three year project to study the interactive effect of spray quality, air amendment, and mode of action on herbicide effectiveness is reported. The objectives of the work were to establish the effect of conventional and air-amended drift reducing sprays on herbicide effectiveness, and to study relationships between weed species and application method on spray deposition. In 2002, laboratory and field studies were conducted. Field studies evaluated 10 different herbicide treatments involving 16 different active ingredients and eight modes of action. Each herbicide treatment was applied at two rates (full label rate and either 0.75 x or 0.5 x, depending on the product), or in the case of Reglone, two rates and two carrier volumes. Herbicide performance was evaluated with visual ratings, weed biomass measurements, weed seed production, and crop seed yield. Six nozzle treatments were distinguished by spray quality (medium, coarse, or very coarse) and air induction (yes or no). Laboratory studies evaluated differences in spray droplet size among nozzles and within pattern locations, and total spray deposition on several weed types. Field results were similar to those from 2000, indicating that herbicide rate affected weed control much more frequently (64% of time) than spray quality (36%) or air induction (5%). Wild oat was more sensitive to all variables than broadleaf weeds. Spray quality measurements indicated that sprays tended to deliver smaller droplets in the central region of the pattern, and coarser droplets near the edge. In particular, droplet numbers dropped significantly at the edges of the spray patterns. It is suggested that greater than 30% overlap may be required to maintain a uniform distribution of droplet size and number under the spray boom. Spray retention of three spray qualities was similar for broadleaf species (tame buckwheat and tame mustard). For easy-to-wet broadleaf targets, spray retention was increased slightly with coarser sprays and air induction nozzles. Air induction also produced more uniform spray patterns, with retention values that were more similar under the nozzle centre and overlap compared to conventional sprays. For conventional nozzles on difficult-to-wet surfaces, the medium spray produced greater retention values than coarse and very coarse sprays. However, for air-induced sprays, coarse sprays were just as effectively retained on difficult-to-wet surfaces as medium sprays. Spray retention was reduced for very coarse sprays.

Executive Summary

Field and laboratory experiments were conducted to study the interactive effects of spray quality, air induction, herbicide mode of action, and herbicide rate on weed control in wheat and canola, and desiccation of lentils.

Field experiments were conducted at the U of S Kernen Research Farm near Saskatoon, and laboratory experiments were conducted at Agriculture and Agri-Food Canada’s Saskatoon Research Centre.

The experiments studied six nozzles: three nozzles were air induced, whereas three were not air induced. These nozzles delivered approximately medium, coarse, and very coarse sprays in each air-amendment category.

Herbicide products were Horizon and DyVel tank mix, Freedom Gold (Assure and Refine tank mix), Everest and Buctril M tank mix, Avenge and Pardner tank mix, Roundup pre-seed, Rustler chem-fallow, Sundance, Accord, Liberty, and Reglone Pro

Weed control was more frequently affected by herbicide rate than application method. Grassy weeds were more sensitive to these variables than broadleaf weeds.

Spray droplet size varied with distance along the x-axis of the nozzle. Low-drift sprays contained fewer droplets overall, and edges of spray patterns contained coarser and fewer droplets than central regions. This observation has implications for overlap of sprays, as a traditional recommendation of 30% overlap will cause regions of suboptimal droplet numbers in the overlap region of the spray. Use of 50% overlap may provide a more uniform distribution of droplet size and density along the boom width.

Spray retention amounts and uniformity were affected by weed type, spray quality, and air induction. Broadleaf weeds were much more efficient at retaining spray, capturing about six to seven times more spray on average than grassy weeds per g dry matter basis. Air induction improved retention uniformity along the width of the boom for broadleaf weeds and it allowed coarser sprays to be used on grassy weeds without loss of retention quantity.

Technical Report

Background and Project Objectives

Management of spray drift continues to dominate in discussions of how to reduce the environmental impact of pesticides. Factors leading to decreased tolerance to drift include greater use of non-selective herbicides during times of acute sensitivity of the ecosystem (i.e. in herbicide tolerant crops), products with greater activity, and more diversification to sensitive special crops. Recent initiatives by the Pest Management Regulatory Agency (PMRA) to protect environmentally sensitive areas (such as shelter belts and water bodies) from drift damage through “buffer zones” can significantly restrict pesticide use on farm land.

New “venturi” nozzle technologies that dramatically reduce spray drift were introduced into Canada in 1997. These nozzles incorporate air into the spray pattern, and reduce drift by up to 95%. Since their introduction, ten different venturi-type nozzle models have become available and these are very popular with applicators. In 2000, new low-drift nozzles that do not use air-amendment were introduced, and these will likely also have good market potential. It is not known how the lack of air-induction will affect biological performance of low-drift herbicide sprays.

The limiting factor to low-drift nozzle adoption is lack of knowledge in efficacy performance. Applicators are reluctant to use application methods that may reduce pest control, for which they assume all risk. Conversely, agrichemical companies are reluctant to endorse low-drift measures if product performance may be compromised. The only way out of this dilemma is to provide good information to all parties. Lowering the risk, coupled with demonstration and communication of effective weed control with low-drift sprays, will enhance adoption of new methods, ultimately protecting the environment. Buffer zones may be reduced for low-drift application methods, providing additional encouragement for applicators to spray in a safe manner.

Objectives:

1. Establish the effect of conventional and air-amended drift reducing sprays on herbicide effectiveness.

2. Identify the limits of spray coarseness for various weed - herbicide combinations;

3. Study relationships between weed species and application method on spray deposition.

LABORATORY STUDIES

Background

Air Induction

Large droplets which contain air inclusions which not only reduce spraylosses to drift and are also claimed but alsoto reduce losses due to reflection from leaf surfaces. This can be explained as follows: for a Research suggests that air induction nozzles produce droplets that maintain velocity during the transfer phase, droplet of a given diameter (say 500 µm), air inclusions will increase the drop diameter, but not its mass. It will therefore travel more slowly (due to increased drag), reducing its kinetic energy. Upon impact with a target, the air inclusions make the droplet less stable, increasing its likelihood of shattering. A shattered droplet can leave a deposit which resembles the deposit of several smaller droplets. Air induction can therefore reduce drift potential without increasing reflection from the target.

Target Characteristics

Leaf angle can have a significant effect on surface retention of pesticides (Wolf et al., 2000). Planophile plants, or species that have leaves approximately parallel to the grounds surface and thus low leaf angles, retain greater amounts of spray. Erectophile plants, which are characteristic of high leaf angles, such as grasses, often have lower interception and retention of herbicides (Spillman, 1984). These losses tend to be significant with hard to wet surfaces. Although species specific, leaf orientation has been found to change towards the horizontal with increasing leaf age (Jensen and Kirknel, 1994). Additionally, Jensen et al. (1994) showed significantly lower deposition on younger growth stages. This effect is particularly significant with very coarse droplets. Young growth stages appear to be smooth in texture thus increasing the probability of repulsion (Spillman, 1984). Older leaf surfaces, are rougher in texture and offer a greater possibility of droplet capture. These effects need to be belanced with the general observation that more mature plants are also more difficult to control.

Leaf surface properties are important in determining spray retention. Leaf hairs and wax can limit the amount of herbicide that can diffuse quickly into the epidermal layers of the plant, thus reducing control (Jensen and Kirknel, 1994). Complex crystalline leaf surfaces are typically difficult to wet (Harr et al., 1991). Difficult-to-wet species have been found to have contact angles of water droplets >110 degrees, whereas easy-to-wet surfaces are characterized by contact angles ................
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